1. Field of the Invention
The present invention relates to a recording head and a recording apparatus. More particularly, the invention relates to an ink jet head and a recording apparatus using the ink jet head. In this respect, recording includes the application of ink or the like (print) for all the ink carriers capable of receiving the application of ink, such as cloth, thread, paper, and sheet materials. The recording apparatus includes all information apparatuses of the various kinds or printers serving as its output equipment. The present invention is applicable to the use of such ink carriers and apparatuses.
2. Related Background Art
As an ink jet method to discharge ink, there has been known the so-called bubble jet method in which ink is rapidly heated when driving heat generating resistive elements arranged on a heater board formed of Si substrate so that ink is discharged from the discharge ports of the recording head.
FIG. 5 is an exploded perspective view which shows the structure of the principal part of a recording head using such a conventional bubble jet method. In FIG. 5, a reference numeral 1 designates a plurality of heat generating elements (not shown) and a heater board (elemental substrate) on which the functional elements are electrically connected to the heat generating elements to drive them selectively; and 2, a wiring board for transmitting to the heater board the signals received from an apparatus having the head mounted on it. This wiring board 2 is electrically connected to the heater board 1 through a wire bonding portion 3. This board is also provided with a card edge connector 2A. The card edge connector 2A is a coupler to connect the apparatus main body (not shown in FIG. 5) and the wiring board 2 electrically.
The heater board 1 and the wiring board 2 are fixed to a base plate 4 by the application of bonding agent. The base plate 4 functions as a positioning board for the heater board dually with respect to the apparatus main body. In general, this plate is formed by Al (aluminum) or other metallic material. On the heater board, plural grooves are formed corresponding to the heat generating elements. This grooved ceiling plate 6 is connected to the heater board to provide liquid paths and a liquid chamber. A reference numeral 5 designates an ink container, which is fixed to the base plate 4, and also, conductively connected to the liquid paths and liquid chamber.
FIG. 6 is a cross sectional view schematically showing the structure of the recording head whose heat generating elements and functional elements are prepared on the same substrate, located near the heater board 1. In FIG. 6, the heater board 1 is formed by an Si substrate layer 1A and an element formation layer 1B. Also, a reference numeral 6 designates the grooved ceiling plate to form the ink paths and liquid chamber; 7, ink; and 8, a recording material to receive the application of ink. Recording is made by the ink droplets 7A to be discharged by the application of heat generated by a heater (not shown). A recording head of the kind, in which its heat generating elements and functional elements are formed on the same substrate, occupies the leading position among the heads available in recent years because it is possible for this kind of head to decrease the number of electrically connected wires between the recording apparatus main body and the recording head even when the number of nozzles (liquid paths) is increased. Here, each of the functional elements is produced by the usual semiconductor fabrication processes. Generally, the substrate layer 1A of the heater board discharges to the apparatus side through the aforesaid wiring board. Therefore, this layer is usable as GND potential.
FIG. 7 is a perspective view which schematically shows one example of the ink jet recording apparatus on which the aforesaid recording head can be installed. In FIG. 7, a reference numeral 13 designates a carriage to hold the recording head 12, which is connected to a part of a driving belt 15 that transmits the driving force of a driving motor 14. The carriage is slidably mounted on two guide shafts 16A and 16B arranged in parallel to each other so as to enable the recording head 12 to reciprocates over the entire width of the recording sheet. Here, when the recording head 12 is installed on the carriage 13, it is electrically connected to the recording apparatus main body through a flexible cable 11.
Now, the recording head shown in FIG. 5 and FIG. 6 is provided with the electrical wiring (circuit) as described above. Therefore, if such recording head is of an exchangeable type, a problem is encountered: electrostatic destruction (ESD) may occur in exchanging heads.
As a countermeasure in this respect, it is conceivable that the recording head is covered with an insulating resin or the like as much as possible. As shown in FIG. 5, however, there is need for the base plate 4 of the recording head to be exposed in order to serve as the electrical connector 2A and the positioning board as well with respect to the apparatus main body. This requirement makes it impossible to cover the head with resin entirely. Now, supposing that this recording head is installed on the recording head shown in FIG. 7, for example, the electrical connector is in a condition that the user is not allowed to touch the connector and couple it to the main body of the recording apparatus, but the base plate 4 is still in a state of being exposed. If the user who is electrostatically charged intends to change the recording heads in this state, the probability is still high that static electricity is transferred to the base plate 4, and then, to the heater board in spite of the insulating layer (bonding agent), thus discharging to the GND (earth) of the apparatus main body through the wire bonding portion 3 and the wiring board 2.
Particularly, in a case of a recording head having the heater board 1 whose substrate layer 1A is connected to the GND through the wiring board as shown in FIG. 6, the probability is higher that the discharge is made by way of paths described above. If the discharge is made through these paths, there is a fear that the wires on the heater board are fused or the elements that are fabricated by the application of semiconductor processes are destructed. As a countermeasure, it is conceivable that the wires on the heater board 1 are made thick so as not to be fused even when an excessive current runs or some other means may be taken to enhance the durability of the heater board 1, but the provision of such measures immediately results in making the heater board 1 larger and invites the problem of increased costs.
As another method, it is conceivable that a metallic member is arranged to surround the recording head 7 shown in FIG. 12 so that discharge is made to the metallic member instead of the base plate 4. This arrangement also results in the increase of part numbers, and immediately invites the problem of increased costs.